Due to its involvement in the human genetic disorder Farber Lipogranulomatosis (“FD”), acid ceramidase (“AC;” N-acylsphingosine deacylase, I.U.B.M.B. Enzyme No. EC 3.5.1.23) is the most extensively studied member of the ceramidase enzyme family. The protein has been purified from several sources, and the human and mouse cDNAs and genes have been obtained (Bernardo et al., “Purification, Characterization, and Biosynthesis of Human Acid Ceramidase,” J. Biol. Chem. 270:11098-102 (1995); Koch et al., “Molecular Cloning and Characterization of a Full-length Complementary DNA Encoding Human Acid Ceramidase. Identification of the First Molecular Lesion Causing Farber Disease,” J. Biol. Chem. 2711:33110-5 (1996); Li et al., “Cloning and Characterization of the Full-length cDNA and Genomic Sequences Encoding Murine Acid Ceramidase,” Genomics 50:267-74 (1998); Li et al., “The Human Acid Ceramidase Gene (ASAH): Chromosomal Location, Mutation Analysis, and Expression,” Genomics 62:223-31 (1999)). Growing interest in the biology of this and other ceramidases stems from the fact that these enzymes play a central role in ceramide metabolism. Ceramide is a signaling lipid that is produced in response to various stimuli (Hannun, “Function of Ceramide in Coordinating Cellular Responses to Stress,” Science 274:1855-9 (1996); Spiegel et al., “Signal Transduction Through Lipid Second Messengers,” Curr. Opin. Cell. Biol. 8:159-67 (1996)). Normally present in low amounts, in response to these factors, ceramide is rapidly produced at the cell surface, leading to membrane re-organization and downstream signaling that results in apoptosis. After stimulation, AC and/or other ceramidases may then hydrolyze ceramide into the individual fatty acid and sphingosine components (Gatt, “Enzymic Hydrolysis and Synthesis of Ceramide,” J. Biol. Chem. 238:3131-3 (1963); Gatt, “Enzymatic Hydrolysis of Sphingolipids. 1. Hydrolysis and Synthesis of Ceramides by an Enzyme from Rat Brain,” J. Biol. Chem. 241:3724-31 (1966); Hassler & Bell, “Ceramidase: Enzymology and Metabolic Roles,” Adv. Lip. Res. 26:49-57 (1993)). Because ceramide degradation is the only source of intracellular sphingosine (Rother et al., “Biosynthesis of Sphingolipids: Dihydroceramide and Not Sphinganine Is Desaturated by Cultured Cells,” Biochem. Biophys. Res. Commun. 189:14-20 (1992)), these enzymes may also be rate-limiting steps in determining the intracellular levels of this compound. Importantly, a derivative of sphingosine, sphingosine-1-phosphate (“S1P”), can counteract the apoptotic effects of ceramide (Cuvillier et al., “Suppression of Ceramide-mediated Programmed Cell Death by Sphingosine-1-phosphate,” Nature 381:800-3 (1996)), leading to the suggestion that ceramidases can be “rheostats” that maintain a proper balance between cell growth and death (Spiegel & Merrill, “Sphingolipids Metabolism and Cell Growth Regulation,” FASEB J. 10:1388-97 (1996)).
Ovulated eggs undergo molecular changes characteristic of apoptosis unless successful fertilization occurs (Marston & Chang, “The Fertilizable Life of Ova and Their Morphology Following Delayed Insemination in Mature and Immature Mice,” J. Exp. Zool. 155:237-52 (1964); Tarin et al., “Long-term Effects of Postovulatory Aging of Mouse Eggs on Offspring: A Two-generational Study,” Biol. Reprod. 61:1347-55 (1999)). While multiple factors, including ceramide, have been characterized as pro-apoptotic elements involved in this process (Perez et al., “A Central Role for Ceramide in the Age-related Acceleration of Apoptosis in the Female Germline,” FASEB J. 19:860-2 (2005); Miao et al., “Cumulus Cells Accelerate Aging of Mouse Oocytes,” Biol. Reprod. 73:1025-1031 (2005); Kerr et al., “Morphological Criteria for Identifying Apoptosis,” in 1 CELL BIOLOGY: A LABORATORY HANDBOOK 319-29 (Julio E. Celis ed., 1994); Gordo et al., “Intracellular Calcium Oscillations Signal Apoptosis Rather Than Activation in in Vitro Aged Mouse Eggs,” Bio. Reprod. 66:1828-37 (2002)), little is known about factors that sustain egg or embryo survival.
The present invention is directed to overcoming these and other deficiencies in the art.